This application claims the priority of Korean Patent Application No. 2002-74121, filed on Nov. 26, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical subscriber network, and more particularly to a method and apparatus for processing Ethernet data in a media access control (MAC) sublayer of an Ethernet passive optical network (Ethernet-PON).
2. Description of the Related Art
Passive optical networks (PONs) represent a network structure which connects access nodes and optical line terminations (OLTs) through optical splitters using a point-to-multipoint configuration. These passive optical networks (PONs) are classified into an ATM-PON and an Ethernet-PON according to information exchange methods with the access nodes. Ethernet PONs represent PONs which transmit Ethernet data frames. In the Ethernet PON, an Emulation sublayer checks medium state signals in order to process a primitive signal received from the physical layer, in a media access control (MAC) sublayer. Here, the Emulation sublayer is also called a reconciliation sublayer (RS). A method for transmitting upstream and downstream Ethernet data frames between the Emulation sublayer and the MAC sublayer will be described hereinafter.
The MAC sublayer of the Ethernet PON includes a sending unit for processing downstream data and a receiving unit for processing upstream data. The sending unit generates a frame check sequence (FCS) for only the Ethernet frames transferred using a multi-point control protocol (MPCP) of a MAC control sublayer. The sending unit modifies the Ethernet frame, transferred from an MPCP function unit executing the MPCP, to have the same phase as data transferred from a PON bridge, and then transmits the resultant Ethernet frame. That is, the sending unit processes two types of Ethernet frames transmitted from different sources, so that the two types of Ethernet frames have the same phase. The receiving unit generates an FCS for 8-bit data processed at a 125 MHz rate, performs address filtering of data, also collects various frame information, and stores the collected data in a management information register.
FIG. 1 is a view of the protocol layer structure of a conventional Ethernet PON.
Optical line terminations (OLTs) and optical network units (ONUs) have the same protocol layer structure, including: a PCS+PMA+PMD sublayer 170 as the physical layer for processing a physical coding sublayer (PCS), a physical medium attachment (PMA), and a physical medium dependent (PMD); a gigabit media independent interface (GMII) sublayer 160; an Emulation sublayer 150; a plurality of MAC (media access control) sublayers 140; a plurality of MAC control sublayers 130; a PON bridge sublayer 120; and an Emulated MAC sublayer 110.
The Emulated MAC sublayer 110 performs upstream and downstream Ethernet frame matching, frame check sequence (FCS) error checking, a PAUSE frame processing, etc. The PON Bridge sublayer 120 performs the basic bridge functions of an Ethernet PON and PON tag management. In the OLT, the MAC control sublayer 130 performs band allocation, scheduling, and work associated with the other MAC controls. According to IEEE 802.3ah, the multi-point control protocol (MPCP) is recommended as a protocol for controlling PON transmission while satisfying Ethernet frame transmission standards. For this reason, the MAC control sublayer 150 is also called an MPCP function unit.
The downstream processing of the multiple MAC sublayers 140 includes receiving a downstream Ethernet frame transmitted from the MAC control sublayer 130, generating an FCS of a control frame for MPCP in the Ethernet frame, inserting an inter frame gap (IFP) into the Ethernet frame, and performing management information base (MIB) counter management for the Ethernet frame. The upstream processing of the MAC sublayers 140 includes performing FCS error checking, address filtering, and MIB counter management for an upsteam Ethernet frame. In the conventional Ethernet PON protocol layer structure shown in FIG. 1, the multiple MAC sublayers 140 and multiple MAC control sublayers 130, classified based on respective LLIDs (logical link identifications), are provided.
An Emulation sublayer 150 performs CRC (cyclic redundancy check) on information included in the preamble of a data frame transmitted from the physical layer, and extracts the LLID, in order to support data frame processing of the upper MAC sublayer 140. An Emulation sublayer 150 in an ONU performs filtering on a received data frame, and transfers the filtered data frame to an upper layer only if the LLID of the received data frame is identical with the LLID allocated to the Emulation sublayer.
The gigabit media independent interface (GMII) 160 is an interface capable of processing Ethernet frames at a rate equal to or less than 1 gigabit/sec. The PCS+PMA+PMD sublayer 170, as the physical layer, provides an interface with an optical module and optical module apparatus suited to the Ethernet PON.
However, because the conventional Ethernet frame processing method is a method for processing general purpose Ethernet frames, the conventional technique can not be used for processing a specific frame including an LLID. In addition, it is not appropriate to apply the conventional Ethernet frame processing method to transmission apparatuses for an Ethernet PON.
Also, in the conventional technique, since the number of MAC sublayers and MAC control sublayers should amount to so many as the number of LLIDS, many more problems exist compared to when using a simplified layer structure of the present invention, especially considering a case in which required LLIDs are further increased by a minimum of 16 and a maximum of 128.